This invention relates to internal combustion crankcase compression engines, and in particular two means for eliminating popping or stalling of such engines at lower rpm's.
Two-cycle internal combustion crankcase compression engines are typical for marine outboard applications. In such engines, fuel, after passing through and being vaporized in the carburator, is passed into sseparate crankcase compartments, each of the compartments being in communication with an individual cylinder of the engine. The fuel is compressed in each of the crankcase compartments before being introduced into the respective cylinder for combustion. In such engines, as exemplified by U.S. Pat. No. 4,244,332, introduction of vaporized fuel into the crankcase is controlled through a reed block assembly.
In smaller such engines, and in particular two cylinder engines having separate crankcase compartments serviced by a common reed block assembly, at low rpm's, the engines can experience what is known as "lean popping" or engine stalling when the engine is throttled back. Lean popping causes rather rough idling of the engine, and is due to unequal pressures between the two crankcase compartments.
In the past, lean popping has been eliminated by means of a dashpot assembly installed on the throttle of the engine to slow return of carburator controls for the engine upon rapid release of the throttle of reduction of the throttle position from a high throttle position to an idle position. Slowing return of the carburator controls prevents the unequal pressures which occur, thus eliminating lean popping or engine stalling at idle speeds.
One problem with a dashpot assembly is the obvious delay introduced during a rapid desired reduction of engine speed from a high throttle position to a speed at or near idle. Another concern is cost since the dashpot assembly does introduce additional components and complexity into the engine.